Television system



M 1933 F. VON OKOLICSANYI 2,158,990

TELEVISION SYSTEM Filed Feb. 4, 1937 5 Sheets-Sheet l M y 15, 1939- F. VON OKOLICSANYI 2,158,990

TELEVISION SYSTEM Filed Feb. 4, 1937 5 Sheets-Sheet 2 I 43'- 45 I 48]] 5] n7 N :2 A H 9 $52 jay an er,-

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TELEVI S ION SYSTEM Filed Feb. 4, 1937 5 s-Sheet 5 4 fmrenfor;

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TELEVISION S'Y-STEM Filed Feb. 4, 1937 5 Sheets-Sheet 4 W F. VON OKOLICSANYH 9 TELEVISION SYSTEM Filed Feb. 4, 1937 5 Sheets-Sheet 5 roas ed May 16, 193 n 2,158,) i

" UN-ITEDSTVATIES PATENT I TELEVISION SYSTEM Franz von Okolicsanyi, Kensington, London,

v England Application February 4. 1931, Serial No. 123.961 In Great Britainjebruary 5, 1938 17.(2laims. (c1. 178'i.1)

The present inventionv relates to a method of lenses is placed a transparent cell 4, tilled with a scanning for television and like systems. 1 1 liquid 5. At one end of the cell is situated a To impart the necessary scanning motion to a piezo-electric crystal 6 which is set into vibration beam of light itisknown to employ moving optical by high frequency alternating electrical energy parts, such as mirror drums, Nipkow discs and the applied via terminals 1 to electrodes 8. Travellike. These methods necessitate the use of at ing compressional waves are thus produced in the least one component moving at a very high speed liquid and their efiect is such that in addition to to accomplish the high speed component of the normal or central image of the slot I in the scanning, and furthermore the line frequency of plane 2, there'is produced a series of side images,

the scanning cannot be easily altered. Other or interference fringes. In-Fig. 2 is shown the 10 scanning methods avoid these disadvantages by central image 9, and the side images l0 thus proemploying a moving electron beam, but with these Qduced by optical interference. As the amplitude methods high electrical voltages are necessary." oi the liquid waves increases. the central image and the operation must take place in a vacuump becomes weaker and the side images become I.) It is also known to employ the Kerr effect to oscilbrighter. If the central image is obscured by late the extraordinary ray which results from means of a stop II. and the light fr m the i double refraction, but the resulting movement is images is collected by a lens I! on to a screen I3, small. the intensity of the light on this screen will vary One object of the present invention is to proin accordance with the amplitude of the liquid vide an improved method of scanning which waves. Obviously the same result will be obg0 avoids the use of high speed moving parts. tained by obscuring the side images and utilizing Another object of the invention is to provide a the lig t fr t central a The le s l2 1 scanning method in which the line scanning irearranged to focus an image of e q d Surface quency can be easily changed at will. on to the screen I3, so that each point on the A further object of the invention is to provide a liquid surfa es th p int H and 5. will be as scanning method in which the synchronisation sepa at y imaged 0n the ee 8- 8-. at

difiiculties associated with normal methods are and the intensity-0f ea image depending avoided. I upon the amplitude of the-waves at the corre- The invention will now be described by way of Spending p t in t c If the high q cy example with reference to the accompanying potentials applied to the crystal are modulated 80 drawings in which Figs. land 2 illustrate the with television signals, then the amplitude of the action of a well known form of light modulating travelling Waves W Va y o point to Point cell; Fig. 3 illustrates a television receiver emalong the len th o t e cell in accordance with bodying the present invention; Fi 4 is the irthe amplitude of the television signals, 1. e., in

cuit diagram of an amplifier and shaping circuit accordance with the brightness of a series 01 adfor the line synchronising impulses; Figs. 5 to '7 J'acent picture Po n lying in a picture lineare explanatory diagrams; Figs 3 and 9 i t t Hence on the screen i3 there will be obtained a an alternative form of television receiver; Fig. 10 Series Of mov g images of t e Picture n s is an explanatory diagram; Fi 11 d 12 m which can be utilized to reconstitute the picture.

trate a modified form of the receiverillustrated in Hitherto this has b accomplished by ep ac 40 Fig. 8; Fig. 13 shows a method of increasing the the Screen 13 With a high Speed Scanning e e member of interference images by using several Such s a rota-tilig mirror drum, which p s to wave trains in one cell; Figs. 14 and 15 illustrate the images o the P cture elements a motion in in plan and side elevation respectively a further the Opposite direction to t e Own motion so that form of television receiver employing the present they are imm on the ng screen. The 46 invention; Figs. 16 and 17 illustrate in plan and above described cell. a d m th d f u ilizin it side elevationrespectively a film transmitter em-t for television purposes more fully bed bodying the present invention; Fig. 1a illustrates inv the specification o J efi 'ees app cation a direct viewing television transmitter embodying Serial the presentinvention; and Fig.l9 illustrates the Methods Of utilizing these cells for v si 50 m t of producing l speed scanning t aid receivers according to the present invention will of the present inv t now be described with reference to Figs. 3 to "7.

Referring to Fig. 1, an image of a light source i v A beam of light from a source 20 passes through in the form of an illuminated slot is focussed in a'Kerr cell, shown diagrammatically at 2| which the plane 2 by means of lenses 3. Between the acts in known manner to modulate the intensity is of the light in accordance with the picture signals,

and then through a cell 22 of the type illustrated in Fig. 1. The cell provides the high speed component of scanning in a manner to be described.

I the latter being fed through a shaping circuit and amplifier 29, to be described later, to the modulator 30 where they modulate high frequency oscillations from the source 3|. The modulator is biassed so that normally the high frequency oscillations are reduced to a very low value, the action of each synchronizing impulse being to permit the generation of a short group of oscillations (Fig. 6). The output of the modulator is fed via terminals 32 to the crystal of the cell 22, short discontinuous groups of waves being generated in the liquid of the cell.

A description of the amplifier and shaping circuit 29 will now be given with reference to Figs.

4 and 5. The circuit comprises three valves V1,'V2 and V3 with resistance-capacity coupling between them. The line synchronizing impulses applied to the grid of valve V1 will have the form illustrated in curve I of Fig. 5. The anode circuit of this valve contains a resistance 33 and a condenser 32 in parallel. Each of the square-topped impulses will charge the condenser 32, which will then discharge through the resistance 33. By suitably choosing the time constant of the circuit 32, 33 and also the relative values of the condenser 32 and resistance 33, the charging time is made equal to the discharging time so that the signals applied to the grid of valve V2 will have the triangular shape illustrated in curve H of Fig. 5. The grid of this valve has applied thereto a negative bias, the value of which is regulated by the variable resistance 34. This bias can be regulated so that the valve V2 transmits only the upper portion of the triangular shape impulses;

for example, the portion above the dotted line in curve ll of Fig. 5. Hence, the impulses applied to the grid of valve V3 will have the shape illustrated in curve ill of Fig. 5. Valve V3 acts as an amplifier, the shape of the impulses in its output circuit being illustrated in curve IV of Fig. 5. Hence, by varying the value of resistance 34 and hence the position of the dotted line in curve H of Fig. 5, the ratio of the space occupied by an impulse to the distance between two impulses can be varied, this ratio becoming smaller as the negative bias on the grid of valve V2 is increased.

In Fig. 6 is illustrated the high frequency wave applied to the crystal of cell 22. It is seen that the normal amplitude of the wave is so small as .to be negligible, the amplitude increasing very greatly each time an impulse is applied to the modulating circuit 30.

Each group of waves generated in the liquid travel of the group of waves through the liquid of the cell. Hence the cell 22 acts in a manner similar to that of an opaque screen with a slot in it, the slot moving in a direction parallel to the axis of the mirror drum 26. Thus elemental areas of the screen corresponding to the original picture elements will be momentarily illuminated. A cell operated to produce this effect will be hereinafter referred to as a "wave-slot cell. The frequency of the high frequency oscillations derived from the source 3| is so chosen with relation to the liquid in the cell 22,, that one group of waves is leaving the crystal at the instant that the preceding group of waves has reached the top end of the cell 22. Also the value of the resistance 33 is adjusted until the ratio of the length of a wave group to the length of the cell is equal to the ratio of the length of a picture element to the length of the picture line. The former ratio determines the degree of definition of which the receiver is capable. The latter ratio is the "definition" of the transmitter. In Fig. 'l in which the rectangle 36 denotes the boundary of the cell or of that part of it that is active in influencing the light passing through it, the waves being propagated from one end of the rectangle to the other. The curve represents the amplitude of the waves at difl'erent points along the cell at an instant of time, the portion 31 indicating the suddent increase in amplitude due to the arrival of an impulse. The ratio of the width of the portion 31 to the length of the rectangle 35 is the definition of the receiver. It will be understood that there is no advantage in making the definition of the receiver higher than that of the transmitter. The best result is attained by the adjustment described above.

If it is desired to employ the light from the central image and to obscure the side images, as described above, then the modulator 30 must be biassed to such an extent that unmodulated oscillations from the terminals 3| is applied to the crystal with full amplitude, the impulses being applied to the modulator in such a sense that they momentarily quench the oscillation. The output from the modulator will thus be represented by a curve which is the inverse of that shown in Fig. 6.

Under these conditions the wave slot cell 22 and the mirror drum 26 cooperate to provide respectively the high and low speed scanning components, and since the light incident upon the screen 25 is modulated with the picture currents by the Kerr cell 2|, the picturewiil be reconstituted.

The apparatus shown in Fig. 3 can be operated in an alternative manner to that described above .to produce the same eflect. This is done simply by applying the shaped line synchronizing impulses existing in the-output circuit of the device 29 to the terminals of the Kerr cell in place of the picture currents and applying the latter to the input of the modulator 30. The amplitude of the Waves in the cell will now .vary along the length of the cell insaccordance with amplitude of successive picture elements, and since the length of the cell corresponds to the length of the picture line, there will be represented in the cell at successive instants of time a complete picture line. A cell operated in this manner will hereinafter be referred to as a modulator cell. The picture line will be imaged on the screen 25 exactly as before, but owing to the fact that the waves are travelling through the liquid, the corresponding images will be travelling across the screen instead of remaining stationary, and hence cannot be observed. Thisis rectified by the action of the Kerr cell, which cannot transmit light in the absence of electrical impulses applied to it. Since these impulses occur only at line frequency, and sincetheir duration time is only that of one picture element (due to the previously described action of the circuit 29) the Kerr cell will act as a shutter and the cell 22 will be intermittently illuminated .at line frequency, so that each picture line is momentarily projected on the screen 25, and no motion of the line can be discerned, since the time of each illumination period is of the order of one picture element. Due to the action of the mirror drum 26, each line will be momentarily projected below the previous line to reconstitute the complete picture. In this case it is clear that a time limitation is imposed upon' the light passing through the cell in contradistinction to the first method of operation, in which a space limitation was imposed upon the light. The shorter the period of illumination is made, the higher the definition becomes. In practice the result is satisfactory if the duration of each flash of light to the time between two flashes approximates to the ratio between the length of a picture element to the length of the picture line.

It is clear that the light eificiency of the apparatus illustrated in Fig. 3 when operated in accordance with this second method will be very poor, since the greater portion'of the light emitted by the source 20 is wasted. This can be improved by utilizing a discharge tube, such as a high-pressure mercury vapour lamp, which lights intermittently at the line frequency instead of continuously, the current consumed and hence the brilliancy being very great at each flash. The Kerr cell or an equivalent shutter controlled by the line synchronizing impulses, then limits the duration time of each flash to the order of that of one picture element. The waste of light can be avoided still further by dispensing with the Kerr cell and employing a lamp which can light intermittently at a frequency in the neighbourhood of line frequency, but in whichthe duration of each period of illumination persists only for a time of the order of the duration time of a picture element, the lamp being controlled by the shaped line synchronizing impulses. Suitable for this purpose are stroboscopic lamps such as described in the article entitled Acold cathode arc-discharge tube in Electrical Engineering, volume 55, No. 7, pages 799,'etc.

A form of receiver employing a wave-slot cell and a modulator cell is shown in Fig. 8. Light ,from a source in the form of an illuminated slit id is passed through the modulator cell 4|, to the terminals42 of which is applied a high frequency oscillation modulated with the picture currents. The slotted screen 43 obscures the central image, the two slots M permitting light from the side images to pass through lens 45 to a wave slot cell 416, the lens t5 focussing an image of the liquid of cell M on to the liquid of cell 46. The terminals ii of this cell are fed with a high frequency oscillation modulated with the shaped line synchronizing impulses, as described in connection with Fig. 3. The slotted screen 48 is designed to permit the passage of light only from the side images produced by the wave slot inthe wave slot cell. Since the slots 44 of the screen 43 each act as a modulated light source, the cell 46 will produce two overlapping sets of interference images,

and hence the screen 48 is provided with two stops on to the surface of the modulator cell.

49 for obscuring the two central images, and slots 50' for permitting the passage of light from the side images. The two screens 43 and 4! are illustrated more clearly in Fig. 9. The lens ll forms animage of the liquid of the cell 48 on the viewing screen 52, the low speed scanner -l8 sweeping this image over the the screen in a direction at right angles to the paper.

Referring now to Fig. 10 in which the rectangle represents the wave slot cell 46 it is seen that an image of the picture modulated waves of the cell 4|, represented by the full curve 54. moves across the cell in the direction of the upper arrow, whilst the wave slot itself, produced by the impulses applied to the terminals 41, and represented by the dotted curve 55, moves at the same speed in the direction of the lower arrow, the relative motion between the two producing the required high speed scanning component. It is clear that exactly the same result will be obtained by interchanging the modulator and wave slot cells, in which case an image of the wave slot is projected It is preferable, though not essential, that the two sets of waves should move parallel to one another in opposite directions as shown in Fig. 10. Thus they may move in the same directionsat different speeds, or alternatively one set of waves may be at an angle, for example 45, to the other set. In the latter case, the resulting picture line would be at an angle to'that normally obtained but this could be corrected by a suitable turning of the two cells with respect to the remainder of the apparatus.

In the arrangement of Fig. 8 it can be arranged that the wave slot 55 moves with a greater speed than the picture modulation 54, so that the time during which the wave slot is active is small compared with the duration time of a picture line.

In this case, for a given degree ,of picture ,definition, thewidth of the wave slot, and therefore the resulting illumination can now be increased. The light source can be arranged to light intermittently and only during the time when the wave slot is active, thereby affecting a saving pf the energy required to produce the light. The line synchronizing impulses are used to control both the wave slot cell and the light source. Alternatively a Kerr cell or equivalent shutter may be used with a constant light source, thereby avoiding the incidence of unwanted stray beams of light during the time when the wave slot is inactive.

An important and useful feature of the receiving arrangements described above is that a stationary picture will be reproduced even when the line scanning frequency at the transmitter alters. Thus, considering Fig. 8, if at the transmitter the line scanning frequency suddenly increases, the length of a picture line as represented by the picture modulations in the cell- 4| will decrease, but this is compensated by the fact that the frequency of the synchronizing impulses applied to the cell will increase, and hence the distance between two successive wave slots will also decrease in the same proportion. Hence, on the screen the reproduced picture will simply contract in thedirection of the scanning lines but will otherwise remain stationary. It is thus clear 68 is a filament lamp provided with a plurality of filaments side by side to provide a source of light having a more or less square shape. The cylindrical lens 62 forms an image of the filament in the liquid of the cell 63 in one plane, whilst in the plane at right angles, the light diverges from the slot 6| to illuminate the face of the cell 63. The lenses of the cell 63 form an image of this slot upon the central opaque portion of the screen 66. The cell 63 contains two crystals 64, 65, situated one above the other. To the crystal 64 is applied an oscillation modulated with the picture currents, so that the upper part of the cell acts as a modulator cell and corresponds to the cell 4| of Fig. 8. The light from the side images passes through the slots of screen 66, is reflected by the prism 61 through the lens 68 to the lower part of the cell, which acts as a wave slot cell and corresponds to the cell 46 of Fig. 8, the line synchronizing impulses being applied as modulations of a high frequency oscillation to the crystal .65. The lens 68 forms an image of the upper part of the liquid surface in the cell63 upon the lower part of the liquid surface, and corresponds to lens 45 of Fig. 8. Also the cylindrical lenses of the cell 63 form images of the slots in the screen 66 upon the two opaque portions of the screen 18, the light being reflected by'means of the mirror 69. Hence, a second interference pattern is produced on the screen 10, the central images being obscured, and the light from the side images passing through the three slots via the cylindrical lens I l l3 and the mirror drum I2 to the screen 14. The operation of this receiver is substantially similar to that illustrated in Fig. 8 'and need not be described in detail. The screen 66, prism 61 and lens 68 may be replaced by the two dotted portions 15 cut from a spherical concave mirror as illustrated in Fig. 12.

The receivers described above have one disadvantage, namely that the quantity of light which can be utilized is somewhat small. Thus in Fig. 8 the lenses 45 and cannot work at their maximum aperture. It is possible, however, to utilize .the full aperture of these lenses by working with several sets of interference images side by side instead of one set of interference images. One method of accomplishing this is illustrated in Fig. 13. In this figure there is shown a light source 16 and cell 18 and two slotted screens TI and 82, these elements corre sponding to the light source, modulator cell and slotted screens shown on the left side of Fig. 8. The light source is. very large in the plane of the paper and can be constituted by a long filament lamp as shown. The screen 1] contains a number of slots each of which acts as a separate light source. The lenses 19 of the cell focus images of these slots on the screen 82 in such a way that the image of each slot is formed on the opaque portion lying between two slots of the screen 82. The cell contains a number of crystals 88 equal in number to the number of slots in the screen 11. For the sake of simplicity only three crystals are shown in the drawings. The crystals are connected in parallel to terminals 8|, a suitable high frequency oscillation modulated with the picture currents being applied to these terminals. The crystals are so arranged that each produces a train of waves in different direction, the direction of the waves being indicated by the arrows 86, 81 and 88. With this arrangement, each wave train will influence only the beam of light which passes at right angles to it; thus the wave train 86 will influence the beam of light 83 coming from the middle slot, whilst the wave'trains 81 and 88 will influence respectively the light beams 84 and 85 coming'from the extreme slots of the screen 11. There will thus be formed in the screen 82 a number of sets of interference'images, each corresponding to one of the light beams issuing from the slots in the screen 11. The central image of each of these sets is obscured by the screen 82 and the light from the side images of all the sets passes through the slots in the screen 82 and is utilized in a manner similar to that described in Fig. .8. It is clear that the remainder of the apparatus will be similar to that shown in Fig. 8, the cell 41 being replaced by a second cell similar to cell 18 of Fig. 13 and the screen 48 of Fig. 8 being replaced by a screen with a larger number of apertures and corresponding to the screen 82. With this arrangement the lenses 45 and 5| in Fig. 8 can be used at their full aperture with a corresponding increase in the amount of light which can be utilized.

In Figs. 14 and 15 is shown an alternative method of increasing the light handling capacity of a receiver. These figures show in plan-and side elevation respectively a television receiver employing one cell 9| which acts as a wave slot cell, the light incident upon the cell being modulated in any suitable manner will be in accordance with the picture currents. This particular arrangement is chosen for illustration in view of its simplicity, and it will be clear that the arrangement can be adapted to any of the receiving methods illustrated with reference to Figs. 3 to 11. To further simplify Fig. 15, the light rays are shown as being transmitted through the reflecting surfaces 93, 95 instead of being reflected by them. The light source 90 in this case has a large size in the plane at right angles to the plane containing the waves in the cell 9i; i. e., its large dimension is at right angles to the large dimension of the light source of Fig. 13. In the plane of Fig. 15 the cylindrical lens 92 forms an image of the light source 90 in the liquid of the cell 9|. In the plane of Fig. 14 the lenses of the cell 9i form an image of the light source 90 on the surface of three mirrors 95, each of these mirrors being provided with an opaque strip. The light emerging from the cell 9! is reflected on to the mirrors 95 by a set of three mirrors 93, which are situated one above the other in the plane of Fig. 15, and are inclined relatively to one another about the axis 94 as shown in Fig. 14. Each of these mirrors will reflect in a different direction the light from one third of the image of the light source in the liquid, this being due to their relative displacement about the axis 94. The top and bottom mirrors of the mirrors 93' are also tilted about their own longitudinal axis as shown in Fig. 15, the effect being that the three portions of the light source image are now brought into line side by side. These three portions are focussed inthe plane of Fig. 14 on the surface of three mirrors 95, these three mirrors also being displaced about the axis 96 which is at right angles to the axis 94. The light from each one third portion of the light source image will produce its own interference pattern in the plane of the axis 96, the central images of these three patterns being obscured by the opaque strips on the mirrors 95. The light from the side images is collected by the lens 91 which focusses an image of the liquid surfaceon the screen 99 via the low speed mirror drum 98. Owing to the fact that the light incident upon the mirrors 95 is coming from diiferent heights which films moves in the direction of the arrow.

in the plane of Fig. 15, it would also be reflected at different heights if a plane mirror were used in place of the mirrors 95. This is corrected by the angular displacement of the mirrors 9! about the axis 96. The function of the two sets of mirrors is to transform the incident beam, which has its large aperture'in the plane containing the di; rection of motion of the low speed scanner (i. e., the plane of Fig. into a beam having its large aperture in the plane containing the direction at right angles tothe low speed scanning direction (i. e., the plane of Fig. 14) since it is only in this plane that the large aperture can be fully utilized. In order to achievethis it is possible to utilize any of thebeam transforming devices described in thespecification of J. H. Jeffree's application Serial No. 3062/35 in place of the two sets of mirrors described above. A still further increase in the light can be obtained by combining the methods illustrated in Fig. 13 with the methods illustrated in Figs. 14; to 15. since a light source can then be arsed which is large in both dimensions.

possible to use for this purpose an oscillograph with a very small mirror, the oscillograph being driven with currents having a saw-toothed wave form and generated by any well known time base circuit controlled by. the picture frequencysynchronizing impulses. In addition to the many obvious advantages, such an oscillograph has the advantage that its amplitude of vibration be-' comes, or canbe made to become, less as the scanning frequency radiated from the transmitter increases. that such an increase will produce a lateral contraction of the received picture when thepresent invention is employed, and due to this decrease in amplitude of the oscillograph, a corre-- sponding vertical contraction can be automatically obtained, thus preserving the original picture ratio.

It must be emphasized that the use of such a small low speed scanner, and in fact, any of the arrangements described with reference to Figs. 13 to 15, only become possible when the, present invention is employed. If an attempt were made to employ them with a system using a normal high speed scanning member the size of this member would have to be increased to such a size as to be impracticable in order to .obtain the necessary light handling capacity.

The application of the inventionto a television transmitter will now be described. In Figs. 16 and 17 there is shown in plan and side elevation respectively a television transmitter for cinematograph films. A light source I00 illuminates a slot ml, the cylindrical lens I 02 forming an image. of the light source in the liquid of a wave slot cell I03, whilst the lenses I04 of the cell form an image of the slot IOI on the screen I01. The cylindrical lens I 00 forms an. image of the liquid of the cell upon the slot IIO whilst the cylindrical lens I09 forms an image of the liquid and of the light source image focussed therin upon' the slot H0. The spherical lens I'II forms an image of the slot IIO upon the film II2 to be scanned,

It has already been pointed out A suitable source of high frequency electrical oscillations is modulated with impulses generated in any well known manner and shaped by means of the circuit illustrated in Fig. 4, the modulation being effected in such a manner that the final output can be, represented by the curve shown in Fig. 6. This outputis applied to the terminals I08 of the crystal I05 and consequently, in the manner already described, a spot of lightis caused can be regulated within very wide limits by adv justing the width of the slit IIO,,which limits the size of the spot in one direction, and by adjusting the resistances 34 of Fig; 4 which limits the size of the spot in the other direction. 'Also the scan ning frequency can be very easily altered by varying the frequency of the impulse generator and the speed of movement of the film. By suitably choosing the frequency of the impulses in relation to the speed of movement of the fllm, normal or interlaced'scanning can be produced at will.

In Fig.18 is illustrated a direct viewing transmitter employing the present invention. The lens H6 forms an image of the object H5 upon the surface of the screen II8, thisimage being swept over the screen by the mirror II! of a low speed oscillograph which is driven by saw-toothed oscillations derived from a suitable timebase circuit at the desired picture frequency. The screen II8 contains a long slot N9, the image of the object being exposed through the slot, line by line, as it is swept over the screen. The light from each picture line is transmitted through a slotted screen I20 and a cylindrical lens I2I to a wave slot cell I22, the lens I2I forming an image of the slot H9 in the liquid of the cell. The screen I20 is provided with a number ofslots each of which acts as a virtual light source, and the lenses of the cell'I22 image these slots upon the slotted screen I23 in such a way that the images fall between the slots of the screen I23. The cell I22 is provided with a number of crystals fed in parallel through the terminals I25, the number of crystals'being equal to the number of slots in the screen I20. The cell and the associated screens I20 and I23 are the same as those illustrated in Fig. 13 and operate in an identical manner. Consequently the light transmitted through each slot of the screen I23 will be the light from the side images ofan interference pattern corresponding to one of the slots of the screen I20. Hence the total light emerging from these slots will be modu- The low speed component of scanning can also longer dimension of each cell lies in a plane which is parallel to the plane of the receiving screen, but whereas the longer dimension of the cell I3I is parallel to the length of the strips of the picture to be projected on the screen, the longer dimensions of the other cells are at right angles to are modulated with impulses derived from generators I39, I40 to provide the desired wave slots. The frequency of the impulses applied to one cell differs from thahof the frequencies applied to the other, these two frequencies being so chosen that each successive line of the picture is momentarily transmitted through two coincident wave slots and is projected on the screen, the point of incidence moving step by step over the length of the cells so that each successive picture line is projected on to the screen immediately below the previous line.

It will be understood that the lenses previously described will have to be interposed in the path of the light beam in order to focus an image of one cell on the next and the slotted screens designed to obscure the central images must be inserted between the cells in the planes numbered I4I, I42 and I43. Also a pair of cylindrical lenses I44, I45 are employed to focus an image of the cell I34 on the screen I46, the lens I44 increasing the size of this image in the plane at right angles ,to the plane of the paper; and the lens I45 reducing the size of the image in the plane of the paper.

Many modifications of the examples described above are possible. For example, in all the receivers described, the television signals which are received as modulations of a carrier wave have been obtainedby demodulating the carrier wave, and are then utilized to modulate a locally generated high frequency oscillation before being applied to the crystals of the cells. Instead of this process it is possible to apply the modulated carrier directly to the crystals. In this case it is desirable to rectify the carrier without demodulation before applying it to the crystal, so that only the half waves of the carrier are applied to the crystal, in order to avoid losing the contrast present in the original picture. ble to avoid the necessity of generating a separate carrier wave and utilizing a modulating circuit at the transmitter, by utilizing the high frequency oscillations applied to the crystal of the wave slot cell. This can be done by applying them to a second cell in the path of the light in such a way that standing waves are produced in this cell. In this case the current produced in the output circuit of the photo-cell will consist directly of a carrier wave modulated with the picture currents. If a so-called electron multiplier photo cell is employed, this modulated carrier current can be radiated directly from the output circuit of this cell.

Also, it is possible to obtain sharper impulses than by the method described with reference to Figs. 4 and 5 by allowing each received impulse to modulate momentarily the frequency as well as the amplitude of the high frequency oscillation,

It is also possithe effect being analogous to that of the well known zone plate.

I claim as my invention:

1. In a television system, apparatus for producing the high speed scanning component comprising a liquid adapted to be illuminated by a beam of light directed thereupon, wave generating means in contact with said liquid for producing therein trains of compressional waves of supersonic frequency travelling in a direction crossing that of a beam of light if directed upon said liquid, thereby resolving such a beam in a portion maintaining its original direction and a portion deviated from said direction, a shield member for selecting one of said portions, optical means for utilizing said selected portion to form an image of said waves on an elemental area of a surface to be scanned, an electrical arrangement for deriving synchronizing impulses of de-' sired line, scanning frequency, and means for utilizing said impulses to control the relation between the duration of illumination of said liquid and the active length of said trains of waves so that said image is periodically and momentarily produced at said line scanning frequency.

2. In a television system, apparatus for producing the high speed scanning component, comprising a liquid adapted to be illuminated by a beam of -light directed upon said liquid wave generating means in contact withsaid liquid for producing therein discontinuous trains of compressional waves of supersonic frequency travelling in a direction crossing that of a light beam if directed upon said liquid, thereby resolving such a beam into a portion maintaining its original direction and a portion deviated from said direction, a shield member for selecting one of said portions, optical means for'utilizing said selected portion to form an image of said waves on an elemental area of a surface to be scanned, an electrical arrangement for deriving synchronizing impulses of desired line scanning frequency, and means for utilizing said impulses to control the length of said trains of waves so that said image is periodically and momentarily produced at said line scanning frequency.

3. In a television system, apparatus for producing the high speed scanning component comprising means for developing an intermittent light beam, a liquid illuminated by said beam, wave generating means in contact with said liquid for producing in said liquid trains of compressional waves of supersonic frequency travelling in. a direction crossing that of said beam, thereby resolving said beam into a portion maintaining its original direction and a portion deviated from said direction, a shield member for selecting one of said portions, a surface to be scanned, optical means for utilizing said selected portion to form an image of said waves on said surface, an electrical circuit for deriving synchronizing impulses of desired line'scanning frequency, and means for utilizing said impulses to control the frequency of said intermittent light beam so that each elemental area of said surface is periodically and momentarily illuminated 10 impulses to control the length of said trains of waves and the, frequency of said intermittent light beam so that each elemental area of said surface is periodically and momentarily illuminated at said line scanning frequency.

5. A television receiver comprising a light source, a surface to be scanned, means for receiving television signals comprising picture signals and line synchronizing signals, two light control devices placed one after the other in the path of the light from said source to said screen, at least one of said devices comprising a transparent cellcontaining a liquid and having a piezoeelectric crystal at one end thereof in contact with the liquid, means for applying said picture signals to' one of said devices and said line synchronizing signals to the other of said devices, the signals applied to said cell being appliedto the pi'ezo-electric crystal in the form of modulations of ahigh frequency electrical oscillation whereby modulated travelling compressional waves are generated in the liquid of said cell and the light emerging from said cell consists of one part which maintains its original direction and a second part which is deviated from said direction, means for selecting one of said parts, an optical system for focussing an image of said waves on said surface, and a low speed scanning member interposed in the path of the light between the second of said devices and said surface.

6. A television receiver comprising a li ht source, a surface to be scanned, means for receiving television signals comprising picture signals and line synchronizing signals; two transparent cells placed in the path of the light from said source to said screen, each cell containing a liquid and having a piezo-electric crystal at one end thereof in contact with the liquid. means for applying said picture signals in the form of modulations of a high frequency electrical oscillation to one of said crystals to generate modulated travelling compressional waves in the liquid of the one cell, means for applying said line synchronizing impulses in the form of modulations of a high frequency electrical oscillation to the other of said crystals to generate modulated travelling compressional waves in the liquid of the other cell. a screen interposed between said cells, two slots in said screen. an optical system for focussing an ima e of said light source on said, screen between said slots. a second screen between the second cell and said surface. three slots in said screen, an optical system for focussing an image of each of said slots of said first screen on said second screen, said images falling between the slots of said second screen. an optical system for focussing an image of said waves in the first cell on the liquid of said second cell, a further optical system for' of the light from said sources to said surface, at 15 8. A television receiver according to claim 6 wherein said two cells are replaced by a single cell having two piezo-electric crystals placed one above the other to generate two trains of travelling waves one above the other in the liquid of the 5 cell, optical means being provided to reflect the light transmitted through one of said trains on to the other of said trains.

9. A television receiver comprising a plurality of light sources or the equivalent arranged side by 10 side in a line, a surface to be scanned, means for receiving television signals comprising picture signals and line synchronizing signals, two light control devices placed one after the other in the path least one of said devices comprising a transparent cell containing a liquid and having piezo-electric means in contact with said liquid, means for applying said picture signals to one of said devices and said linesynchronizing signals to the other of 20 said devices, the signals applied to said cell being applied to said piezo-electric means in the form of modulations of a high frequency electrical oscillation, said means being arranged to generate a plurality of trains of modulated travelling com- 25 pressional waves, the number of said trainsbeing equal to the number of said light sources, all of said trains travelling in the plane containing said light sources but in different directions, whereby each train is effective in influencing the light from 30 one of said sources to produce one part of the light which maintains its original direction and a second part which is deviated from said direction, means for selecting one of said parts of the light from all of said sources, an optical system for focussing an image of said waves on said surface, and a low speed scanning member interposed in the path of the light between the second of 'said devices and said surface.

10. A television receiver comprising a light 40 source means for developing from said source a light beam having a large aperture in one plane, a surface to be scanned, means for receiving television signals comprising picture signals, line synchronizing signals and picture synchronizing sig-'- 45 nals, two light control devices placed in the path of said light beam between said source and said surface, at least one of said devices comprising a transparent cell containing a liquid with a piezoelectric crystal at one end thereof in contact with 50 consisting of one part which maintains its original 69 d rection and second part which is deviated from said direction, means for selecting one of said parts. optical means for forming an image of said waves on said surface, a low speed scanning'member controlled by said picture synchronizing sig- 65 nals interposed in the path of the light between said cell and said surface, the direction of scanning of said member being in a plane at right angles to the plane containing the direction of travel of said waves, and a stepped optical trans- 70 forming device between said cell and said member for transforming the large aperture of said beam into the plane containing the direction of travel of said waves.

11. A television receiveraccording to claim 10 7 wherein said transforming device comprises a series of mirrors angularly displaced about an axis at right angles to the direction of travel of said waves, and a second series of mirrors angularly displaced about an axis at right angles to said first mentioned axis.

12. A television receiver according to claim 10 wherein said low speed scanning member comprises an oscillograph with a small mirror, said oscillograph being actuated with currents having a saw-toothed wave form derived from a timebase circuit controlled by said picture synchronizing impulses.

13. A television transmitter for cinematograph films comprising a light source, a film to be scanned, a transparent cell in the path of the light between said source and said film, a liquid in said cell, a piezo-electric crystal in contact with said liquid at one end of said cell, means for generating electrical impulses of a desired frequency, means for generating high frequency electrical oscillations, means for modulating said oscillations with said impulses and applying the modulated oscillations to said crystal to produce discontinuous groups of traversing compressional ,waves in said liquid whereby the light emerging from said cell comprises one part which maintains its original direction and asecond part which is deviatedfrom said direction, means for selecting one of said parts, optical means for focussing an image of said waves on a long slot, the length of said slot being parallel to the traversing direction of said waves, means for focussing an image of said slot on said film, means for moving said film in a direction at right angles to the length of said slot, means for shaping said impulses whereby the length of a wave group can-be ad-- justed in relation to the distance between two successive wave groups, light sensitive means situated behind said film, and a transmitting circuit connected to said light sensitive means.

14. A transmitter according to claim 13 wherein the width of said slot is adjustable.

15. A television transmitter comprising means for forming an image of an object to be televised on a screen, a long slot in said screen, a low speed scanning member for sweeping said image over said screen in a direction at right angles to the length of said slot, a light sensitive member, a transmitting circuit connected to said light sensitive member, and interposed in the path of said light from said screen to said light sensitive member in the order named a second screen, a first optical system, a second optical system, a transparent cell containing a liquid and having piezoelectric means in contact with said liquid, and a third screen, said second screen having at least one slot, the length of said slots being at right angles to the length of the slot of said first screen, said first optical system forming an image of the slot of said first screen in said liquid, said second optical system forming images of the slots of said second screen on said third screen, said third screen being provided with a number of slots which interleave with the images of the slots of said second screen, said piezo-electric means being energized with a high frequency electrical oscillation modulated with impulses to produce in said liquid a number of trains of travelling compressional waves in the form of discontinuous groups, the number of trains being equal to the number of slots in said second screen, and the direction of travel of each of said trains lying in the plane containing the slot in said first screen and being different from one another.

16. A television receiver comprising a light source, a surface to be scanned, and arranged in the path of the light between said source and said surface in the order named a first transparent cell containing a liquid and a piezo-electric crystal in contact with said liquid, and a second and third transparent cells also containing a liquid with a piezo-electric crystal in contact therewith the axes of said second and third cells being parallel to one another and at right angles to the axis of said first cell, the crystal of said first cell being energized with high frequency electrical oscillations modulated with picture signals derived from a transmitter, the crystals of said second and third cells being energized with high frequency electrical oscillations modulated with electrical impulses, the frequency of the impulses applied to said second cell being different from those applied to said third cell, whereby the light emerging from each cell comprises one part which maintains its original direction and a second part which is deviated from said direction, means being provided after each cell to select one of said parts, and further optical means being provided to focus an image of the liquid in said first cell on the liquid of said second cell, to focus an image of the liquid of said second cell on the liquid of said third cell, and to focus an image of the liquid of said third cell on said surface to be scanned, the difference in the frequency between said electrical impulses being so chosen that an image of the waves in said first cell is momentarily projected on said surface in successive positions one below the other to reconstitute the picture on said sursaid beam, a liquid in said cell, means for producing in said liquid high frequency travelling compressional waves modulated in amplitude in accordance with said picture signals whereby the light emerging from said cell consists of one part which maintains its original direction and a second part which is deviated from said direction, means for selecting one of said parts, an optical system for utilizing said selected part to form an image of said waves on said surface, and a low speed scanning member interposed in the path of the light between said cell and said surface.

FRANZ VON O KOLICSANYI. 

